1. Field of the Invention
The present invention relates to a charge coupled device (CCD) input circuit which operates according to the fill and spill principle and which comprises an input diode, several input electrodes, and several shift electrodes arranged behind the input electrodes.
2. Description of the Prior Art
CCD input circuits, which are operated according to the fill and spill principle, also simultaneously serve as charge amplifiers. By virtue of the fact that the input collector has an enlarged surface area, as compared with the CCD shift electrodes, the specific charge can be increased. Since, however, the entire charge quantity, consisting of a "fat zero" and the signal component, must be received by a CCD electrode, the operating point must be set low for the input, corresponding to the amplification. Only the a.c. component is to be amplified and not, however, an undesired d.c. component of a respective charge. With increasing amplification, the working point of the input drifts into the start-up slope, as a result of which distortions occur.
A linearization of the CCD input has heretofore been achieved by means of "dipping" or by means of feedback or regeneration--cf. e.g. N. Weste and J. Mavor: "M.O.S.T. amplifiers for performing peripheral integrated circuit functions", printed in the periodical Electronic Circuits and System, 1977, Vol. 1, No. 5.
Surface CCD's (SCCD) having uniform oxide thicknesses are known, which are operated according to the fill and spill principle, which manifest a double surface charge amplification. Since the signal must flow over a threshold, only half the frequency of the surface potential is available for the input electrodes, as compared with a CCD electrode. The surfaces of the control gates, and of the first CCD electrodes, are therefore twice as great as the subordinate CCD electrodes, cf. e.g. C. H. Sequin and A. M. Mohsen: "Linearity of Electrical Injection into Charge-Coupled Devices", published in the IEEE Journal of Solid-State Circuits, Vol. SC-10, No. 2, April 1975, pp. 81-92. It is disadvantageous here that the optimum operating point for the input lies at half the full drive.